Thursday, August 24, 2006

Bush Approval: Harris 34%, Hotline 39% (or 42%)

Two new polls split the difference, leaving estimated approval pretty stable. A new Harris poll, taken 8/18-21/06 finds approval at 34% and disapproval at 65%. Harris has a substantial negative house effect of -2.94, so that 34% should not be taken as evidence for decline in approval. In fact, the previous Harris poll taken 8/4-7 and the one before that taken 7/7-10 also found approval at 34%. This result then, is quite compatible with a story of stable approval ratings, rather than decline. And adjusted for the house effect, suggest approval is really around 34+2.94 or about 37%, which is quite close to my trend estimator.

The second poll of the day is the Hotline poll, taken 8/17-20/06, which finds approval at 39% and disapproval at 58%. That is a one point rise in approval (and one point decline in disapproval) since their 7/20-23 poll. The Hotline house effect is +1.72, so adjusting for that also produces an estimated approval of about 37%. For once, we have glorious agreement among (house adjusted) polls!

The estimated trend in approval of President Bush with these two new polls stands at 37.4%, a small adjustment from the previous estimate of 37.6%. The graph also shows that the trend line is currently estimated to be quite flat, trending neither up nor down for some while. (I caution that the "old blue" estimator has had some trouble figuring out what direction the trend has been moving since June. For some while the data kept it moving slowly up. Then we went through a little while when it looked to be declining. Now the data suggest flat is the best story. Sometime in October we'll have a good idea of what really happened this summer!

Two points are worth mentioning. The Hotline poll found approval/disapproval at 39/58 among registered voters. PollingReport.com reported these figures. Among likely voters the Hotline found approval/disapproval at 42/56. RealClearPolitics.com chose to use this result in their list of approval polls, without any indication that they were reporting a subsample result. I have no objection to reporting both results (something neither of these sources did) but presenting only the LV subsample without an indication that this was for less than the full sample seems dubious to me. In principle every poll of adults could also produce results for RV and LV subsamples. The norm for presidential approval is to report the results for the full sample, however that was defined, and to indicate what population that sample represents. RealClearPolitics.com does an excellent job of linking to sources for the poll results, but in this case I think they made a poor editorial call.

The Harris poll house effect also deserves comment. At -2.94 the Harris poll has the largest negative house effect of all 22 pollsters for which I currently estimate house effects. Before leaping to a conclusion of bias, I want to point out that Harris is one of the few polling firms that uses a four point approval scale: Excellent, Good, Fair, Poor, rather than the more common dichotomous approve/disapprove. It is entirely reasonable that the middle two categories here can provide a "halfway house" between what would register as approve and disapprove on the dichotmous indicator. "Fair" can be attractive for unhappy Republicans, for example, who might reluctantly stick to "approve" on the dichotomous measure. So the negative house effect for Harris should be understood as a combination of house effect AND question wording (response options) effect. As the graph above makes clear, Harris tracks the trend in approval quite well, but with a systematic downward shift for the house/question effect. Before tossing out acsusations of bias, one should consider other reasons for the large house effect.

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About Me

I am co-founder of Pollster.com and founder of PollsAndVotes.com.
I am also a professor of political science at the University of Wisconsin, where I teach statistical analysis of polls, public opinion and election results. Data visualization is central to my approach to analysis.
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